Electromagnetic light-modulating device



March 3, 1931. O O CECCARINI 1,794,513

ELECTROMAGNETIC LIGHT MODULATING DEVICE Filed Jan. 31, 1930 2Sheets-Sheet l swam dot 0Za 22d0 0 (6064/2528 Patented Mar. 3, 1931UNITED STATES PATENT OFFICE OLINDO O. GECOARINI, OF BEVERLY HILLS,CALIFORNIA, ASSIGNOR T METRO- GOLDWYN-MAYER CORPORATION, OF CULVER CITY,CALIFORNIA, A CORPORATION OF NEW YORK ELECTROMAGNETIC LIGHT-MODULATINGDEVICE Application filed January 31, 1980.. Serial No. 424,839.

This invention relates to an electromagnetic light valve adapted tobeemployed in modulating light during photographic recording of sound. Theinvention particular- 6 1y relates to a light valve of sturdy construetion which has a natural period of frequency incapable of producingannoying audible sounds, and which maintains its spacing position andmechanical characteristics without 10 impairment under strenuous workingconditions.

Heretofore, light valves employed in sound recording generally consistedof an armature carrying a pole piece having a minute slot therein, thearmature carrying bridge members over which a thin metallic loop wasstretched, a portion of the loop comprising two parallel ribbon portionsin spaced relation. The slot in the armature is generally about eightmils wide by 256 mils long. The metallic ribbon or tape is only 6 milswide and 0.3 mils thick, the two ortions of the loop being spaced so asto mm a slit 2 mils wide. A single electromagnetic coil was employed.

The minute metallic ribbons used in valves of the ,prior artnecessitated extreme care in setting, and very often under the influenceof oscillatory currents of high amplitude, the ribbons were displacedrelatively to each other so that the opening therebetween was changedfrom the customary opening to an opening of smaller or greater width. Ifone or both of the ribbons had been shifted so as to widen the slit,then the quantity of light passing through the valve in the unmodulatedcondition became greater, thereby materially affecting the distinctnessand volume of the record produced.

- An object of this invention is to disclose and provide anelectromagnetic light valve in which relatively heavy strips areemployed without decreasing the operating range of the valve.

Another object is to disclose and provide a light valve assembly whichpermits ready adjustment.

A still further object is to disclose and provide an electromagneticlight valve in which the light modulating elements are activateddescribed, but embraces all such changes and by flux variations of anelectromagnetic circult, without passing a current through the lightmodulating elements.

Another object is to disclose and provide a sturdy light valveconstruction which may be. readily transported, moved or shifted andwhich is not crltically sensitive to tempera ture changes. i

A still further object is to disclose and provide a light valve whichmay be employed in the pro notion of variable area or variable densitysound records.

A still further object is to disclose and provide an electromagneticlight valve in which a vibratory element is caused to vibrate under theinfluence of a magnetic flux which is varied by the oscillatory currentwhich it is desired to record.

Other objects, uses and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of one preferred form of the apparatus, it being understoodthat the invention is not limited to the device specificallymodifications as come within the skill of the art.

In describing the illustrative form of this invention, reference will behad to the appended drawings, in which:

Fig. 1 is a diagrammatic representation of an arrangement of elementsemployed during the recording of sound, on a continuous film.

Fig. 2 is an enlarged side elevation of one form of electromagneticlight valve.

. Fig. 3 is a plan view of the light valveshown in Fig. 2. V

Fig. 4 is an end elevation, partly in section, of the light valve shownin Figs. 2 and 3, the section being taken along line 44 of Fig. 2.

Fig. 5 is a longitudinal section taken along line 5-5 of Fig. 3.

As shown in Fig. 1, the sound recording 95 equipment may comprise afixed light source 1, a condensing lens system 2, a light modulatingdevice 3 provided with a fixed slot through which the light is passed,an'ob ective lens system' i, and means 5 for passmg'a 1.00

continuous film 6 thereby, upon which the light modulated by the device3 is recorded.

The light modulating device embraced by this invention is illustrated inFigs. 2 to 5 inclusive, and preferably comprises a yoke 7 provided witha suitable surface 8 adapted to seat upon a stationary base having apredetermined relation with the light source lens systems and film movidevice 5. The yoke 7 is preferably provide with outwardly extending flans 9 adapted to receive and support the lock assembly, generallyindicated at 10. Theyoke 7 may also include a bracket 11 provided with alens receiving member 12, said lens receiving member 12 being adapted toreceive the condenser lens 2.

The block assembly preferably comprises-twoopposed recessed blocks 13and 13'. Blocks 13 and 13' are preferably provided with recesses 14communicating. with a smaller aperture 15, said smaller apertures facingeach other in the block assembly. The opposing upper and lower faces ofthe blocks 13 and 13 ma also be provided with recesses 16 and 17. Thepartitions 18 dividing recess 15 fromi the recesses 16 and 17 arepreferably curved as indicated at19 so as to form a curved rest for astrip of magnetic material 20. These strips of magnetic material 20 arepreferably held in a clamp member such as the member 21, provided withan upper serrated surface 22,. a clamp pad 23 being provided having asimilar serrated surface. The clamp pad 23 may be held in firm contactwith the clamp member 21 in any suitable manner, such as for example, bymeans of a screw 24.

The clamp member 21 may be provided with a curved or semi-cylindricalrotuberance 25 adapted to be received in a c amp seat 26 keyed into orformed in the block 13 and preferably in the portion 18 of the block 13.The clamp member 21 may be adjustably positioned by means of a screw 27threadedly mounted in a support28 firmly held by or attached to theblock 13. Inasmuch as the clam members 21 are in the form of'a bell cranlever pivoting at 25, the tension in the strips of ma etic material 20may be adjusted to a nicety by regulating the screw 27 which rests uponthe surface of one of the legs of the clamp 21. X

The recess 14 of the blocks 13 is adapted to receive an exciting coil30, said coil being provided with a core 31. Preferably, the core 31 hasits axis parallel to the longitudinal axis of the strip of magneticmaterial 20. Core members 32 and 33 are preferably connected to the endsof the core 31, said core members extending through the aperture 15 inthe block 13. The core members 32 and 33, during a portion of theirlength, are preferably parallel to each other, as for example theportions 32' and 33' in the port 15. The core members 32 and 33 preferaly terminate in close proximity to each other so as to form a gapindicated at 34. The ends of the coremembers 32 and 33 preferablyapproach, but do not protrude beyond the plane connectin the outermostedges of the portions 18 of t e block 13. In other words, they do notcontact with, but are merely in close proximity to the strips ofmagnetic material 20. 7

Voice current coils 35 and 36 are carried by the core members-32 and 33,and are preferabl positioned around the parallel core mem er portions 32and 33. These voice current coils 35 and 36 may be either connected inseries or parallel, but in such direction as to produce an additiveefi'ect insofar as magnetic flux is concerned. Oscillatory current fromsuitable amplifiers, which in turn are supplied with current frommicrophones, is sent through these voice coils. The space between theends of the core members 32 and 33, and particularly the outer surfaceof the voice current coils 35 and 36, may be covered by a plate 37 ofnon-magnetic insulating material such as for example, a phenolcondensation product.

The block members 13 are preferably con-- nected together in spacedrelation and means are provided for adjustably positioning the bloc s 13and 13' in such spaced relation. Such means may comprise connectingplates 40 and 41, the plate 40 being connected to the block 13, whereasthe plate 41 is connected to the block 13. The plates 40 and 41 may beconnected to their respective blocks in any suitable manner, as forexample, by means of screws 42. It is to be understood that a similarset of plates 40 and 41 is connected to the upper surfaces of the blocks13 and 13 as well as to the lower surfaces.

The plates 40 and 41 are preferably provided with ofi-set portions 43and 44, respectively, adapted to come in sliding contact with eachother, the portion 44 fitting into a dove-tail roove 45 formed in theportion 43. Minor adjustments between the plates 40 and 41, andtherefore,.between the portions 43 and 44 may be made b means. of asuitable headless screw 46 a apted to come into threaded engagement withan internally threaded aperture 47in the member 44, the screw 46 beingrotatably connected to but longitudinally immovable in the member 43.

The screw 46 may be rotatably held in the member 43 by means of aplurality of screws 48 provided with smooth cylindrical ends of smallerdiameter than said screw 48, said I ably held together by means ofinterlocking plates 40 and 41. -This block assembly as a unit may thenbe mounted in the yoke 7 as follows.

End plates and 51 adapted to contact with the outer surfaces of theblocks 13 and with the inner surfaces of the interlocking plates 40 and41 are provided. Said plates may be connected to the blocks 13 by meansof suitable screws 52, and may also be connected to the upper and lowerinterlocking.

plates 40 and 41 by means of screws 53. The end plates 50 and 51 arepreferably provided with flanges 54, each of said flanges being providedwith a slot 55, said flanges 54 being adapted to rest on the flanges 9of the yoke 7.

The end plates 50 and 51 may then be connected to the yoke 7 by means ofbolts 56 passing through the slots 55 in the flanges 54 of the endplates5O and 51, the bolts 56 coming into threaded engagement with theflanges 9 of the yoke 7 as indicated at 57. The block assembly may thenbe adjustably positioned with reference to the yoke (while said bolts 56are still loose) by means of set screws 58 at right angles to the bolts56, said set screws 58 passing through the flanges 9 of the yoke 7 andcontacting with the outer surfaces of the end plates 50 and 51.

In order to facilitate the adjustment of plate 40 and 41 relatively toeach other, an aperture 59 may be provided in the yoke 7 said aperturebeing in alinement with the longitudinalaxis of the adjustment screw 46,thereby permitting the insertion of a suitable implement for themanipulation of the adjustmentscrew. Similarly, an aperture 60 may beformed in the base 8 of the yoke, said aperture being in alinement withthe set screw 49.

It is to be understood that suitable binding posts, such as the bindingposts 61 and 62,

are provided, said binding posts permitting electrical connections to bemade with the exciting coils 30 and with the voice coils 35 and 36. Thevoice coils are preferably connected in series. 7 j

While a. predetermined current is passed through the exciting coils 30,the strips of magnetic material 20 are placed under tension by suitablemanipulation of the adjusting screws 27. The tension should besuflicient to definitely prevent the strips of magnetic material 20 fromcontacting with the ends of core members 32 and 33 under the influenceof the greatest flux concentration which the mechanism may be subjectedto, but insuflicient to prevent the strip of magnetic material 20 frombeing afiected by variations in the flux. In other words, the strip 20should be movable toward or away from the ends of core members 32 and 33under the influence of variations in the flux, thereby changing theeffective gap between the ends of core members 32 and 33 and changingthe reluctance of the magnetic circuit.

When a voice current is passed through the voice current coils 35 and36, the quantity of flux across the gap will be varied, thereby eitherdrawing the magnetic strip 20 closer to the ends of the core members 32and 33, or permitting the tension. of the magnetic strip 20 towithdraw'the strip from the ends of the core members. In this manner thestrips of magnetic material 20 may be caused to vibrate toward and awayfrom the ends of the core members 32 and 33, said vibrations beingsynchronous with the changes in the current passing through the voicecoils, the amplitude of the vibrations of the magnetic stripsQO beingregulated by the amplitude of the voice current. V,

The strips of magnetic material 20 are preferably provided with maskingmeans 63, said masking means being carried by each of the magneticmembers 20 and extending substantially at right angles to the plane ofthe magnetic strips 20. Furthermore, the mask 'ing means 63 shouldpreferably lie in substantially the same plane and each of said maskingmeans should be preferably provided with a true, smooth and sharp edge.The distance between the edges of the masking means 63 may be varied,depending upon the size of the slit or opening through which the fullymodulated light will pass. The inner edges of the masking members 63influence either the width or the length of the slot, thereby graduatingor modulating the total quantity of light passing through the slit andbeing impressed upon the continuous film or other substance receivingthe record of the voice current.

If, {or example, the fixed slit has its longitudinal axis lying in thehorizontal planet whereas the boundaries or adjoining edges of themasking means 63 are vertical, a record of the double envelope type(variable area) may be produced. If only one of the strips of magneticmaterial 20 is caused to vibrate ormod ulate the light (as bydeactivating the exciting coil and voice current coils in one of theblocks 13), then a variable area record of the single envelope type maybe obtained.

If, however, the longitudinal axis'of the fixed slit is parallel to theadjoining inner edges of the masking members 63, then a variable densityrecord may be produced.

The strips 20 are preferably made of spring steel or other magneticmaterial capable of being placed under appreciable tension, and having ahigh modulus of elasticity. Strips 20 need not necessarily be made ofmagnetic material, however, as the strips as a whole may be made ofnon-magnetic elastic material carrying targets such as the masking means63 in those portions of the strip which :oppose the gap between the endsof the'core members.

It is to be understood that the voice current coils 35 and 36 and theexciting coils 30 are properly insulated from the blocks 13 and rigidlypositioned in said blocks. In order to facilitate the positioning of thecoils in the recesses of the block, members 64 may be provided, saidmembers 64 being outwardly extending extensions of the core members 32and 33. These members 64 may then be attached or connected to the blocks13 as by means of the screws 65. Furthermore, in order to conservespace, a recess 66 may be formed in the end plates 50 and 51, saidrecess being adapted to receive the ends of the exciting coils 30.

It will thus be seen that an electromagnetic light valve has beenprovided, said valve consisting of two opposing recessed blocks, each ofsaid blocks containing an'exciting coil and core members, said coremembers carrying voice current coils.

Furthermore, each of said blocks is provided with a strip of magneticmaterial lying in front of the gap formed between the ends of the coremembers. Means have been provided for clamping and placing the strips ofmagnetic material under tension.

Furthermore, means have been provided for adjustably positioning theblock members relatively to each other, thereby permitting carefulcontrol as to the spacing of adjoining strips of magnetic material 20 orthe distance separating the masking members 63. The invention has alsoprovided for means for shifting the entire block assembly relatively toa yoke or relatively to a fixed slot or lens such as, for example, thelens carried by the extension 11 of the yoke 7. Although a specific formof apparatus has been described in detail, it is to be understood thatthe invention is not limited there- ,to. Numerous changes andmodifications of design may be made by those skilled in the .inproximity to each other so as to form a gap, woice current coils mountedaround each of said core members, a strip of magnetic materialpositioned in operative relation before the gap between the ends of eachof said pair of core members, and means for placing said strip underlongitudinal tension.

2. An electromagnetic light valve including two opposed exciting coils,spaced core members extending from said coils toward each other, theends of said cores terminating in proximity to each other so as to forma gap, voice current coils mounted around each of said core members, astrip of magnetic material positioned in operative relation before thegap between the ends of each of said pair of core members, means forplacing said strips under tension, and means for adjust ably positioningsaid coils and magnetic strips relatively to each other.

3. An electromagnetic light valve including two opposed exciting coils,spaced core members extending from said coils toward each other, theends of said corps terminating in proximity to each other so as to forma gap, voice current coils mounted around each of said core members, astrip of magnetic material positioned in operative relation before thegap between the ends of each of said pair of core members, means forplacing said strips under tension, means for adjustably positioning saidcoils and magneticstrips relatively to each other, and masking meanscarried by each of said magnetic strips, said masking means lying in thesame plane and substantially at right angles to the plane of saidmagnetic strips, and-means for adjustably positioning said excitingcoils and strips of magnetic material relatively to each other.

4. In an electromagnetic light valve, the combination of two opposingrecessed blocks, an exciting coil positioned :in each of said blocks, acore in said exciting coil, core members connected to each end of saidcore, said core members terminating in proximity to each other so as toform a gap, voice current coils carried by said core members, a strip ofmagnetic material under tension carrie by each of said blocks, saidstrips passing immediately in front of the ga between the ends of saidcore members, an means connecting said blocks, said means includingmeans for adjustably positioning said blocks relatively to each other.

5. An electromagnetic light valve comprising a yoke, a pair of opposedrecessed blocks, means connecting said blocks, said means 1neludingmeans for adjustably positioning said blocks closer or farther apart soas to form a block assembly, means for connecting V said block assemblyto said yoke including means for adjustably positionin said blockassembly with res ect to said-yo e, an excit-" ing coil in each 0 saidblocks, opposed core members extending from said coils toward eachother, voice current coils 'mounted around said core members, a strip ofmagnetic material removably connected to each of said blocks andpositioned in operative relation before the gap between the ends of saidcore members, means for placing said magnetic strips under tension, andmasking means carried by each of said magnetic strips, said maskingmeans lying in the same plane and siibstantially at right angles to theplane of said magnetic strips.

6. An electromagnetic lightvalve comprising two opposed recessed blocks,means for connecting and adjustably positioning said blocks relativelyto each other so as to form a block assembly, a yoke, means forconnecting said block assembly to said yoke including means for adjustably positionin said block assembly with respect to said yo e, anexciting coil in each of said blocks, a core in each of said coils, coremembers connected to each end of said core, said core members for aportion of their length extending in parallel spaced relation at rightan les to said core, and terminating in proximity to each other so as toform a gap, voice current coils carried by the parallel portions of saidcore members, a strip of magnetic material carried by each of said blockmembers in operative relation before the gap between the ends of saidcore members, means for placing said strips of magnetic material undertension, and masking means carried by each of said magnetic strips, saidmasking means lying in the same plane and substantially at right anglesto the plane of said magnetic strips.

7. An electromagnetic light valve includ-' ing an exciting coil, a corein said coil, said core being provided with ends terminating inproximity to each other so as to form a gap, voice current coils mountedaround each of said core members, and a strip of elastic materialpositioned in operative relation before the gap between the ends of saidcore, said strip being provided with a magnetic portion carried therebyadapted to be actuated by variations in flux across said gap, and meansfor adjustably placing said strip of elastic material under a lon'tudinal tension.

Signed at Culver City, alif., this 28 day of December, 1929.

' OLINDO O. CECCARINI.

